U.S. Pat. No. 6,367,864 B2 granted to Lloyd Rogers, Jr. et al. Apr. 9, 2002 discloses a power operated lift gate that has at least one power unit for raising and lowering the lift gate. The power unit comprises a fixed linear guide channel and a follower that moves in the guide channel. The follower is universally connected to one end of a rod that has an opposite end universally connected to the lift gate. The follower is moved in the guide channel by a flexible drive member that is attached to the follower and that is driven in a loop by a bi-directional drive unit. The drive unit includes a bidirectional electric motor, an electromagnetic clutch and suitable gear sets that are not described in detail. The flexible drive member may be a chain, a drive cable or a slotted drive tape. The electromagnetic clutch is optional and normally deenergized so that the lift gate can be opened and closed manually without the necessity of back driving the electric motor.
U.S. Pat. No. 6,367,199 B2 granted to David A. Sedlak et al. discloses a power operated lift gate that has a power unit in which the follower is a rack bar that is driven directly by a bi-directional drive unit. The rack bar is universally connected to one end of a rod that has an opposite end universally connected to the lift gate. The drive unit includes a bi-directional electric motor that has a worm gear output that drives a first gear set. The first gear set in turn drives an electromagnetic clutch which drives a second gear set that drives the rack bar. The electromagnetic clutch is normally de-energized so that the lift gate can be opened and closed manually without the necessity of back driving the electric motor.
Published International Patent Application WO 01/83247 A2 of Atoma International Corp. discloses a power operated lift gate in which a slideable lift gate carriage 40 is selectively latched to a power guide carriage 50 for power operation. The power guide carriage 50 is moved by a flexible drive member 64 that travels in a loop. The flexible drive member 64 is driven by a bi-directional electric motor 58 which drives a transmission gear 60 via a gear box (unnumbered). The gear set in the gear box is not described in detail. The lift gate carriage 40 is normally unlatched from the power guide carriage 50 so that the lift gate can be opened and closed manually without back driving the electric motor.
As illustrated above, power operated lift gates are normally raised and lowered by an electric motor that operates some sort of mechanism via one or more gear sets. The gear sets reduce the speed of the electric motor which is usually in excess of 3000 rpm to about 30 rpm so that the lift gate is opened or closed at a speed of about 9-13 degrees per second. This requirement for considerable speed reduction of about 12 to 1 generates two needs or desirable characteristics for the drive unit. The primary desire or need is for a quiet and economical speed reduction on the order of 12 to 1. The secondary desire or need is to operate the lift gate manually and preferably without including an electromagnetic clutch or other device to disconnect the electric motor to eliminate back drive.